Cell-cell adhesion is a fundamental feature of multi-cellular systems. The goal of this proposal is to analyze how individual epithelial cells recognize neighboring cells to form mutual cell-cell adhesion while rejecting self-contact. Homophilic adhesive receptors on two opposing cells rapidly bind to form a cell-cell adhesion, yet the same receptors on two thin protrusions originating from the same cell surface do not. This self-awareness of individual cells suggests that cells can distinguish the chemically identical surface of neighboring cells from their own. We hypothesize that the self-recognition mechanism is mechanically regulated, and that the cadherin complex is a mechano-sensing complex that detects external forces, thereby providing a signaling cue for mutual cell adhesion. In the absence of external forces, the mechano-signal is off, and leads to the elimination of self-contacts. Using innovative micro-fabricated substrates to control self-contacting events, we will analyze the formation of self-contacts and the subsequent elimination of self-contacting sites. Furthermore, we have developed miniature force sensors to detect forces at the adhesive contacts and directly test our hypothesis. Our findings will also highlight how mutual cell-cell adhesion forms between neighboring cells. Once we understand the fundamental processes of self and other recognition by cells, our goal is to develop therapeutic agents that alter cell- cell adhesion and can be used to prevent cancer cell invasion or pathogen infection. PUBLIC HEALTH RELEVANCE: Regulation of cell-cell adhesion plays critical roles in development and homeostasis of multi-cellular organisms. The goal of this proposal is to analyze how individual epithelial cells recognize neighboring cells to form mutual cell-cell adhesions while rejecting self-contact. One potential outcome of the proposed research will be the development of advanced therapeutic agents that prevent cancer cell invasion or pathogen infection.